Energy expenditure during continuous intragastric infusion of fuel

Influence of intragastric formula infusion rate on resting thermogenesis was evaluated in 24 healthy subjects. Metabolic rate (M) was measured by indirect calorimetry following an overnight fast. Subgroups then received a continuous intragastric infusion of a formula diet at three levels: submaintenance (mean +/- SEM, 1.02 +/- 0.04 times fasting M, n = 6), maintenance (1.39 +/- 0.01 times fasting M, n = 20), or supramaintenance (2.77 +/- 0.2 times fasting M, n = 14). Formula inflow was started in the evening, and intraprandial M was measured throughout the following day. Relative to fasting, submaintenance and maintenance infusions produced no detectable change in M. With supramaintenance infusion, M increased significantly (10.1%, p less than 0.05) above fasting level. Hence during continuous formula infusion a rise in M above fasting occurs only when rate of energy infusion exceeds rate of thermal energy losses. These results have implications in regard to energetic efficiency of continuous fuel infusion relative to intermittent food or formula ingestion.